1. Field of the Invention
This invention pertains to vehicle safety, and more particularly to apparatus that controls the steering of wagons.
2. Description of the Prior Art
Four-wheel wagons and trailers have been used for many years. They typically include a frame supported by a pair of fixed back wheels and a pair of steering wheels. The steering wheels turn on respective horizontal axles. The steering wheels are connected to a tongue by which the wagon is towed. The tongue is pivotally connected to the wagon frame. Pivoting the tongue rotates the steering wheel axles to steer the wagon. Such wagons are especially popular as farm vehicles, because they are versatile, rugged, and well suited to be towed by a tractor for hauling a variety of cargos.
In some wagons, the steering wheel axles are fixed to each other, and the axles rotate about a single vertical axis in response to pivoting the tongue. In other wagons, the steering wheel axles are independent of each other. The axles are connected to each other by a steering mechanism to rotate in unison about respective vertical axes in response to pivoting the wagon tongue.
Despite their popularity, four-wheel wagons have the undesirable characteristic of being potentially unstable when they are towed. In the past, towing speeds were slow. Changes in the direction of travel of a horse, tractor, truck, or other towing vehicle were easily accommodated by the steering wheels as the changes in direction were transmitted to them by the tongue. In recent years, more powerful tractors and better roads have resulted in considerably higher towing speeds. Under those conditions, the problem of wagon swaying from side to side has become noticeable. If the tractor speed is too great, even small and transient steering changes can set up an unstable situation in which the wagon sways violently from side to side. In some instances, even passing a front wheel over a stone or similar bump can cause swaying problems. That is especially true with modern wagons that employ low-friction kingpins on separate axles for the steering wheels.
A related problem is that along with higher towing speeds, wagons have increased in size. They therefore are capable of carrying heavier loads then in the past. When going down a hill, a heavily loaded wagon tends to push the tractor and create the potential for jackknifing.
Attempts have been made to cure swaying problems of towed vehicles. For example, U.S. Pat. Nos. 3,273,911; 3,294,421; 4,165,885; 4,306,734; and 4,402,523 show stabilizing devices in which fixed assemblies are connected between a semi-trailer and a towing vehicle. U.S. Pat. Nos. 3,400,948 and 3,519,287 teach adjustable friction pads interposed directly between a trailer tongue and a plate on the towing vehicle. None of the mechanisms of the above-mentioned patents is suitable for controlling the steering of four-wheel trailers and wagons.